JPH0114887B2 - - Google Patents

Abstract

The invention relates to a process for purifying, by treatment with an acid ion exchanger and, if desired, a basic ion exchanger, the methanol employed in the preparation of formaldehyde.

Description

[Detailed description of the invention]

The present invention relates to a method for purifying methanol used in the production of formaldehyde. In order not to unduly impair the activity and lifetime of the silver catalyst, the starting materials required for the production of formaldehyde must be very pure (see, for example, DE 2323758). The methanol or methanol/water mixture used for the reaction virtually always contains, in addition to a large number of organic substances, a large number of inorganic compounds, which for example promote side reactions that reduce the yield or poison the catalyst. Acts as. It is therefore necessary to purify the methanol before oxidation, to use very pure water for methanol/water production, or to subject the methanol/water mixture to a subsequent purification step. Therefore, DE 1235881 discloses a process for the production of formaldehyde, in which, before removing the fraction below the boiling point of methanol,
During and/or afterwards, and before the reaction to give formaldehyde, the crude methanol is treated with alkali. A similar purification method is also disclosed in British Patent Specification No. 344,796. According to this patent specification, crude methanol containing, for example, trace amounts of iron as impurities is likewise treated with alkali. However, purification using alkali produces large amounts of strongly alkaline effluent, the removal of which requires considerable technical outlay and detracts from the cost and efficiency of the purification process. Another possible means of purifying crude methanol consists of treatment with oxidizing agents. For example, the purification of crude methanol by treatment with chromic acid is disclosed in British patent specification no. , and purification by treatment with ozone-containing gases is disclosed in German Publication No. 1152392. It has been published in Germany that the purification of crude methanol by treatment with oxygen or hydrogen peroxide in the presence of substances with a large surface area, such as silica gel, diatomaceous earth, alumina, earthy marcasite or activated carbon, is particularly effective. It is mentioned in Specification No. 1231677. However, the purification methods described above have the disadvantage that effluent problems arise when using chromic acid or permanganate. Additionally, trace amounts of chromic acid and permanganate remaining in the treated methanol can impair the activity of sensitive silver catalysts. The use of ozone or hydrogen peroxide during the treatment of crude methanol does not offer any advantages, firstly because these compounds are relatively expensive chemicals and they cannot be recovered after treatment and secondly because This is because only oxidizable substances can be removed thereby. German Publication Specification No. 2323758, column 4, 14-29
Despite the purification of crude methanol using the above compounds as seen from the lines, the lifetime of the silver catalyst and the yield and space/time yield of pure formaldehyde obtained using the catalyst are still unsatisfactory. , because some of the impurities contained in the crude methanol are not removed and it deactivates the catalyst during the reaction. Methanol or methanol to be oxidized/
Process for the purification of methanol or methanol/water mixtures used in the production of formaldehyde, characterized in that the water mixture is treated with an acid ion exchanger and, if appropriate, with a basic ion exchanger, before vaporization. has now been discovered. The acidic ion exchangers used in the process according to the invention are based on crosslinked polystyrene resins containing sulfonic acid groups (strongly acidic ion exchangers) or crosslinked polystyrene resins containing carboxyl groups. Commercially available acidic, porous or gel-type, H-form cation exchangers based on polyacrylic acid (weakly acidic ion exchangers), such as Ullmans Encyclopedi del.・Technician Hemi (Ullmanns)
Encyklopa¨die der technischen Chemie), 4
Edition, Vol. 13, pp. 279-346. In the method according to the invention, strongly acidic macroporous
Porous cation exchangers are preferably used. The basic ion exchangers used are based on cross-linked polystyrene or polyacrylamide resins containing quaternary ammonium groups (strongly basic) or cross-linked containing amide groups. commercially available basic, porous or gel-type anion exchangers based on polystyrene or polyacrylamide resins (weakly basic), such as Ullmann's Encyclopedia der Technissien. Hemy, 4th edition, 13
Vol., pp. 279-346. Strongly basic, large-porous anion exchangers are preferably used in the method according to the invention. For treating methanol or methanol/water mixtures in the process according to the invention, approximately 100 to 200
An acidic ion exchanger of 150 to 180 is used. If these amounts of acidic ion exchanger are used, the yield of anhydrous or aqueous methanol is approximately 500 to
10000/hour, preferably 2000-5000/hour. Of course, smaller or larger amounts of acidic ion exchanger can also be used, with a corresponding decrease or increase in the output of anhydrous or aqueous methanol. The treatment of methanol or methanol/water mixtures with acidic ion exchangers is generally carried out at temperatures of about 0 to 60°C, preferably 15 to 40°C, and the process is advantageously carried out under normal pressure. Ru. Methanol or methanol to be reacted/
If the aqueous mixture is further treated with a basic ion exchanger, 100 to 200, preferably 150
~180, a basic ion exchanger is used.
Here too, suitably smaller or larger amounts of basic ion exchanger can be used, with a corresponding reduction or increase in the output of anhydrous or aqueous methanol, of course. If the above amount of basic ion exchanger is used, the production of anhydrous or aqueous methanol is approximately 300-3000/
hours, preferably 400 to 800/hour. Treatments with basic ion exchangers usually result in a
It is carried out at a temperature of 70°C, preferably between 20 and 65°C and under normal pressure. However, the process can also be carried out under an increased pressure of about 0.1 to 5, preferably 2 to 3 bar;
Temperatures of 90-100°C are most advantageous. The use of pressure is advantageous because it allows the yield of methanol or methanol/water mixtures to be increased considerably without compromising purification activity. If aqueous methanol is used in the reaction, its concentration is about 50-90, preferably 55-70% by weight. Treatment of methanol or methanol/water using acidic and optionally basic ion exchangers can be carried out in conventional ion exchange equipment and according to conventional process methods. The methanol or methanol/water mixture can be treated first with an acidic ion exchanger and then, if necessary, with a basic ion exchanger. Of course, the reverse processing method is also possible. It is preferred for practical reasons to treat first with an alkaline ion exchanger and then with an acidic ion exchanger. Furthermore, methanol or methanol/
The treatment of the water mixture can also be carried out in a mixed bed or stratified bed apparatus. The treatment of methanol or methanol/water mixtures according to the invention can be carried out continuously or discontinuously. For example, aqueous methanol (concentration of methanol,
(approximately 56% by weight), methanol was heated at 40 to 100℃,
preferably at 50-60° C. and under a pressure of up to about 10 bar, pumped at a rate of 4000/h into a vessel filled with 1200 ml of strongly basic ion exchanger and then in this way It can be carried out by passing the treated aqueous methanol at room temperature and under a pressure of up to 10 bar at a rate of 4000 m/h into a vessel filled with 200 molar strongly acidic ion exchangers. The aqueous methanol obtained by this method can then be directly vaporized without further purification and converted to formaldehyde over a silver-catalyzed catalyst. For the production of formaldehyde by oxidation over silver catalyst of methanol or methanol/water mixtures treated according to the invention, continuous or non-continuous production of methanol or methanol/water mixtures from a vaporizer sump product consisting of methanol or methanol/water mixtures is possible. Continuously withdrawing a partial stream, treating this partial stream with an acidic and optionally basic ion exchanger, and then using the partial stream for vaporizing methanol or a methanol/water mixture It is particularly advantageous to return the gas to a vaporizer. The acidic or basic ion exchangers used in this step are the acidic and basic ion exchangers already mentioned and described above. The treatment of the partial stream removed from the vaporizer bottom product is carried out using the acidic and possibly basic ion exchanger already used in the treatment of the fresh methanol or methanol/water mixture passed to the vaporizer. This can be done by a method of passing. However, the treatment of the partial streams can also be carried out separately with acidic and optionally basic ion exchangers. Generally about 500-1500/hour, preferably 800-1500/hour
1000/hour of the vaporizer bottom product is passed through an acidic and optionally basic ion exchanger, the amount of substreams treated depending on the amount of ion exchanger used and the size of the ion exchange bed. Depends on.
Partial stream treatment is usually carried out at temperatures of about 60-70°C. In comparison with the processes hitherto known from the state of the art for producing formaldehyde from methanol, the methanol to be reacted is purified, for example by distillation or by treatment with an alkali or an oxidizing agent. The method according to which the catalyst life is substantially increased (German publication
2137938 to at least 166 days according to the method according to the invention, noting that for the latter the catalyst was still sufficiently active but the test had to be terminated due to technical failures. ) and achieve a high yield of formaldehyde. Furthermore, the treatment of methanol or methanol/water mixtures according to the invention makes it possible to reduce the residual content of methanol in formaldehyde to below 1% by weight (determined by gas chromatography). Since only small amounts of methanol remain in the formaldehyde, the formaldehyde can be subjected in virtually all cases directly to the subsequent reaction, with methanol not being a problem. As a result of the increased yield of formaldehyde obtained by the process according to the invention and as a result of the relatively long catalyst service life obtained, the capacity of existing plants is increased by about 10%, which is another economic advantage. The treatment of methanol in the process according to the invention is carried out using an ion exchanger consisting of an organic polymer, so that trace amounts of ion exchanger material are dissolved in the methanol and thereby sensitively impair the activity of the silver catalyst. It was very surprising to those skilled in the art that the lifetime of the silver catalyst was unexpectedly increased considerably and the yield of formaldehyde was improved, although it was necessary to assume that It is the right thing to do. The following examples are intended to illustrate the method according to the invention. Example Aqueous distilled methanol for the production of formaldehyde (% methanol content, approximately 56% by weight)
continuously at 15-30° C. of strongly acidic cation exchangers in the H form based on polystyrene/divinylbenzene resins containing sulfonic acid groups (e.g. Lewatit SC108, S100, SP112 and SP120).
Commercially available as; Filling amount: 300
output: 4000/h) and then sent directly into the vaporizer of an industrial formaldehyde plant. In addition, the product under the vaporizer pot is 1000
It was circulated continuously by pumping at a rate of 120 g/hr into a vessel filled with a strongly acidic cation exchanger (form H). Air is also added. The methanol/water mixture vaporized in a vaporizer was sprayed onto the silver catalytic catalyst described in Example 1 of German Patent Specification No. 1285995. The reaction at the catalyst is carried out under a pressure of approximately 150-300 mbar and at a temperature of 660-670 °C.
It was carried out using a mixture consisting of Kg/h of methanol vapor, 1586 Kg/h of water vapor and 4020 Kg/h of air. The reaction gases - formaldehyde, water and residual methanol - were cooled in a reaction cooler and then liquefied in a conventional absorption plant, and the exhaust gas was further washed with water, which was reused for the absorption of formaldehyde. During an operating time of 166 days, a formaldehyde solution of approximately 37.5% strength by weight with a residual methanol content of 0.6-0.9% by weight was continuously obtained. The table below shows how the residual methanol content in the formaldehyde solution changes during this time.

Table: During this operating time, the formaldehyde yield varied between 89 and 91% of theory. Aqueous methanol for conversion, which has been purified by distillation but still contains trace amounts of iron carbonyls (approximately 1.5 mg Fe/), is treated with a strongly acidic ion exchanger to remove iron carbonyl compounds from the methanol. If treated in addition to a strongly basic ion exchanger, the formaldehyde solution obtained had a residual methanol content of 0.6-0.9% by weight. Formaldehyde yields varied between 89 and 91% of theory. The treatment with a strongly acidic ion exchanger and the treatment with a strongly basic ion exchanger were carried out under the same conditions as below: Filling amount: 300 Production yield: 4000/hour Temperature: 15-30℃ The test was carried out at 166 Days later it had to be terminated due to a technical failure. At that point the catalyst was still fully active. The catalyst was virtually free of troublesome metallic or carbonaceous deposits. Comparative Example Aqueous distilled methanol (methanol content, approximately 56% by weight) for the production of formaldehyde was fed directly into the vaporizer of an industrial formaldehyde plant at room temperature, and air was simultaneously blown into the vaporizer. The silver catalyst is German Patent Specification No. 1285995
It corresponded to the catalyst described in Example 1 of the issue. The reaction at the catalyst takes place under a pressure of about 100-300 mbar and at a temperature of 650-680 °C, at 2060 °C.
It was carried out using a mixture consisting of Kg/hr methanol vapor, 1586 Kg/hr water vapor and 4020 Kg/hr air. The reaction gases - formaldehyde, water and residual methanol - were cooled in a reactor cooler and then liquefied in a conventional absorption plant, and the exhaust gas was further washed with water, which was reused for formaldehyde absorption. During an operating time of 80 days, a formaldehyde solution of approximately 37.5% strength by weight with a residual methanol content varying between 1.0 and 1.8% by weight was continuously obtained. The table below shows how the residual methanol content in the formaldehyde solution changes during this time.

Table: During this operating time, the formaldehyde yield varied between 86 and 89% of theory. The activity of the catalyst decreased with increasing operating time, as indicated by the increasing content of residual methanol in the formaldehyde solution produced. The catalyst contained many extraneous metals and was further contaminated by carbon deposits.

Claims (1)

[Claims] 1. A method for producing formaldehyde by oxidizing methanol or a methanol/water mixture over a silver catalytic catalyst in the gas phase, the methanol or methanol/water mixture to be oxidized being treated with acid ions before vaporization. A method characterized in that it is treated with an exchanger and, if necessary, a basic ion exchanger. 2. Acidic, macroporous or gel-type materials based on cross-linked polystyrene resins containing sulfonic acid groups or based on cross-linked polyacrylic acids containing carboxyl groups. ,H
2. A method according to claim 1, characterized in that a cation exchanger of the form is used. 3 Basic bases based on cross-linked polystyrene or polyacrylamide resins containing quaternary ammonium groups or based on cross-linked polystyrene or polyacrylamide resins containing amino groups. 2. Process according to claim 1, characterized in that a macroporous or gel-type anion exchanger is used. 4. Process according to claim 1 or 2, characterized in that the treatment with an acidic ion exchanger is carried out at a temperature of 0 to 60°C. 5 Treatment using basic ion exchanger at 0-70℃
The method according to claim 1 or 3, characterized in that it is carried out at a temperature of . 6 Treatment with basic ion exchanger 0.1-5
4. Process according to claim 1, characterized in that it is carried out at a pressure of 1 bar and a temperature of 90 to 100<0>C. 7. Withdrawing a partial stream from the vaporizer bottom product consisting of methanol or a methanol/water mixture;
Claims 1 to 6 characterized in that this partial stream is treated with an acidic ion exchanger and, if necessary, with a basic ion exchanger, and then the partial stream withdrawn is returned to the vaporizer. Any method described.